Aside from the actual need to file a return, what's the NRST have that a simple flat tax wouldn't (aside from the "underground economy" angle, which mostly involves skirting taxes for illegal things that should be left up to states to decide whether or not they're illegal anyway)?
Well first off it would reduce the price of our exports by cutting out many hidden embedded taxes in their cost of production, advertising and shipping....a flat tax does not change that it may reduce complexity some but still taxes income rather than consumption.
I am not against the idea of a flat tax, but just try to get one through to law. It won't happen. Look, even a simple cut in taxes is viewed as opressing the "working man" (Really only those who work marginally and would receive less of a handout via the IRS in the form of credits & the EIC).
I think the flat tax is a great idea. It has far less of a chance of passsage, though. It will never happen in our lifetimes.